The present invention is an improvement upon the subject matter of my U.S. Pat. No. 4,441,499, issued Apr. 10, 1984. That patent discloses a dynamic foot support or "orthotic" platform which helps the foot move through various critical positions or stages within the walking cycle. The dynamic platform facilitates the shock absorbing and adaption stage of the gait cycle which is called "pronation." Pronation occurs during heel contact until the midstance, full weight bearing stage of the human gait. During the human gait an eversion of the heel occurs in the subtalar joint (that is, the heel bone) and in the bone directly above it (the talus). As pronation occurs, the midtarsal joint becomes more easily "unlocked." (The midtarsal joint is comprised of the composite calcaneal cuboid and talar navicular joint). This unlocking or free swinging attitude gives the foot its adaptability and enhances its ability to absorb shock. However, if pronation continues beyond midstance the foot becomes inefficient for thrust off. As a result the forefoot becomes hypermobile at all its joints and therefore more susceptible to all the wear and tear conditions and acquired deformities associated with mechanical foot disorders. The motion that is opposite to pronation, i.e., suppination or inversion of the feet, causes the axis of the articulation (calcaneal-cuboid, talarnavicular) to become oblique making the midtarsal joint lock up, which in turn makes the foot a rigid lever for thrust off.
Many of the prescribed or over-the-counter orthotics attempt to limit or eliminate the natural pronation. The orthotic of the '499 patent facilitates pronation by assisting the foot in moving from pronation toward the position of suppination that is necessary to attain efficient toe off for forward propulsion, and thereby reduces the hypermobility of the forefoot. The '499 patent discloses a platform having longitudinal cuts which form finger-like portions which are referred to as "rays." (The foot also has rays which consist of each metatarsal and its articulation with its corresponding cuneiform bone, with the exception of the fourth and fifth metatarsals which articulate with the cuboid.) The rays of the platform are cut far into the platform, from the toe or leading end of the platform all the way to the heel. The platform rays disclosed in the '499 patent extend past the ends of the rays of the actual foot and in fact past the midtarsal joint articulations.